Iron base alloys containing aluminum can have ordered and disordered body centered crystal structures. For instance, iron aluminide alloys having intermetallic alloy compositions contain iron and aluminum in various atomic proportions such as Fe.sub.3 Al, FeAl, FeAl.sub.2, FeAl.sub.3, and Fe.sub.2 Al.sub.5. Fe.sub.3 Al intermetallic iron aluminides having a body centered cubic ordered crystal structure are disclosed in U.S. Pat. Nos. 5,320,802; 5,158,744; 5,024,109; and 4,961,903. Such ordered crystal structures generally contain 25 to 40 atomic % Al and alloying additions such as Zr, B, Mo, C, Cr, V, Nb, Si and Y.
An iron aluminide alloy having a disordered body centered crystal structure is disclosed in U.S. Pat. No. 5,238,645 wherein the alloy includes, in weight %, 8-9.5 Al, .ltoreq.7 Cr, .ltoreq.4 Mo, .ltoreq.0.05 C, .ltoreq.0.5 Zr and .ltoreq.0.1 Y, preferably 4.5-5.5 Cr. 1.8-2.2 Mo, 0.02-0.032 C and 0.15-0.25 Zr. Except for three binary alloys having 8.46, 12.04 and 15.90 wt % Al, respectively, all of the specific alloy compositions disclosed in the '645 patent include a minimum of 5 wt % Cr. Further, the '645 patent states that the alloying elements improve strength, room-temperature ductility, high temperature oxidation resistance, aqueous corrosion resistance and resistance to pitting. The '645 patent does not relate to electrical resistance heating elements and does not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
Iron-base alloys containing 3-18 wt % Al, 0.05-0.5 wt % Zr, 0.01-0.1 wt % B and optional Cr, Ti and Mo are disclosed in U.S. Pat. No. 3,026,197 and Canadian Patent No. 648,140. The Zr and B are stated to provide grain refinement, the preferred Al content is 10-18 wt % and the alloys are disclosed as having oxidation resistance, and workability. However, like the '645 patent, the '197 and Canadian patents do not relate to electrical resistance heating elements and does not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
U.S. Pat. No. 3,676,109 discloses an iron-base alloy containing 3-10 wt % Al, 4-8 wt % Cr, about 0.5 wt % Cu, less than 0.05 wt % C, 0.5-2 wt % Ti and optional Mn and B. The '109 patent discloses that the Cu improves resistance to rust spotting, the Cr avoids embrittlement and the Ti provides precipitation hardening. The '109 patent states that the alloys are useful for chemical processing equipment. All of the specific examples disclosed in the '109 patent include 0.5 wt % Cu and at least 1 wt % Cr, with the preferred alloys having at least 9 wt % total Al and Cr, a minimum Cr or Al of at least 6 wt % and a difference between the Al and Cr contents of less than 6 wt %. However, like the '645 patent, the '109 patent does not relate to electrical resistance heating elements and does not address properties such as thermal fatigue resistance, electrical resistivity or high temperature sag resistance.
Iron-base aluminum containing alloys for use as electrical resistance heating elements are disclosed in U.S. Pat. Nos. 1,550,508; 1,990,650; and 2,768,915 and in Canadian Patent No. 648,141. The alloys disclosed in the '508 patent include 20 wt % Al, 10 wt % Mn; 12-15 wt % Al, 6-8 wt % Mn; or 12-16 wt % Al, 2-10 wt % Cr. All of the specific examples disclosed in the '508 patent include at least 6 wt % Cr and at least 10 wt % Al. The alloys disclosed in the '650 patent include 16-20 wt % Al, 5-10 wt % Cr, .ltoreq.0.05 wt % C, .ltoreq.0.25 wt % Si, 0.1-0.5 wt % Ti, .ltoreq.1.5 wt % Mo and 0.4-1.5 wt % Mn and the only specific example includes 17.5 wt % Al, 8.5 wt % Cr, 0.44 wt % Mn, 0.36 wt % Ti, 0.02 wt % C and 0.13 wt % Si. The alloys disclosed in the '915 patent include 10-18 wt % Al, 1-5 wt % Mo, Ti, Ta, V, Cb, Cr, Ni, B and W and the only specific example includes 16 wt % Al and 3 wt % Mo. The alloys disclosed in the Canadian patent include 6-11 wt % Al, 3-10 wt % Cr, .ltoreq.4 wt % Mn, .ltoreq.1 wt % Si, .ltoreq.0.4 wt % Ti, .ltoreq.0.5 wt % C, 0.2-0.5 wt % Zr and 0.05-0.1 wt % B and the only specific examples include at least 5 wt % Cr.
Resistance heaters of various materials are disclosed in U.S. Pat. No. 5,249,586 and in U.S. patent application Ser. Nos. 07/943,504, 08/118,665, 08/105,346 and 08/224,848.
U.S. Pat. No. 4,334,923 discloses a cold-rollable oxidation resistant iron-base alloy useful for catalytic converters containing .ltoreq.0.05% C, 0.1-2% Si, 2-8% Al, 0.02-1% Y, &lt;0.009% P, &lt;0.006% S and &lt;0.009% 0.
U.S. Pat. No. 4,684,505 discloses a heat resistant iron-base alloy containing 10-22% Al, 2-12% Ti, 2-12% Mo, 0.1-1.2% Hf, .ltoreq.1.5% Si, .ltoreq.0.3% C, .ltoreq.0.2% B, .ltoreq.1.0% Ta, .ltoreq.0.5% W, .ltoreq.0.5% V, .ltoreq.0.5% Mn, .ltoreq.0.3% Co, .ltoreq.0.3% Nb, and .ltoreq.0.2% La. The '505 patent discloses a specific alloy having 16% Al, 0.5% Hf, 4% Mo, 3% Si, 4% Ti and 0.2% C.
Japanese Laid-open Patent Application No. 53-119721 discloses a wear resistant, high magnetic permeability alloy having good workability and containing 1.5-17% Al, 0.2-15% Cr and 0.01-8% total of optional additions of &lt;4% Si, &lt;8% Mo, &lt;8% W, &lt;8% Ti, &lt;8% Ge, &lt;8% Cu, &lt;8% V, &lt;8% Mn, &lt;8% Nb, &lt;8% Ta, &lt;8% Ni, &lt;8% Co, &lt;3% Sn, &lt;3% Sb, &lt;3% Be, &lt;3% Hf, &lt;3% Zr, &lt;0.5% Pb, and &lt;3% rare earth metal. Except for a 16% Al, balance Fe alloy, all of the specific examples in Japan '721 include at least 1% Cr and except for a 5% Al, 3% Cr, balance Fe alloy, the remaining examples in Japan '721 include .gtoreq.10% Al.